Page:Popular Science Monthly Volume 76.djvu/13

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9
HALLEY'S COMET.

The "Principia" appeared in 1687. So far as the conclusions there reached apply to the subject before us, the labor of adapting the theoretical results to numerical form and applying them to the practical problem of orbit computation, fell to Edmund Halley.

Halley, a contemporary and friend of Newton, occupies a very prominent place in the history of astronomical and physical science. Among other important discoveries and researches, may be mentioned the long inequality of Jupiter and Saturn, the proper motions of the stars, the secular acceleration of the moon's motion, method of determining the solar parallax by observations of transits of Venus, researches on terrestrial magnetism, and his epoch-making work on the motions of comets.

Halley's Comet.

No. Observed Perihelion. Authority. Calculated
Perihelion.
Authority.
(1) 11 B. C. Oct. 9, Jul Hind
(2) 66 Jan. 26 "  "
(3) 141 March 29 "  "
(4) 218 April 6 "  "
(5) 295 April "  "
(6) 373 Beg. Nov.? "  "
451 July 3 " Laugier
(8) 530 Beg. Nov.? " Hind
(9) 608 End Oct.? "  "
(10) 684 Oct. "  "
11  760 June 11 " Laugier June 15 Crommelin-Cowell
12  837 March 1 " Pingré Feb. 25 " "
(13) 912 Beg. April " Hind July 19 " "
14  989 Sept. 12 " Burckhard Oct. 9 " "
15  1066 April 1 " Hind March 27 " "
16 1145 April 19 "  " April 6 " "
17  1222 Aug. 22 " Crommelin-Cowell Sept. 10 " "
18  1301 Oct. 23 " Hind Oct. 26 " "
19  1378 Nov. 9 " Laugier
20  1456 June 8 " Pingré-Celoria
21  1531 Aug. 26 " Halley
22  1607 Oct. 27 Greg.  " Oct. 27 Lehmann
23  1682 Sept. 14 "  " Sept. 15  "
24  1759 March 13 " Various March 13 Rosenberger
25  1835 Nov. 16 "  " Nov. 15 Pontécoulant
26  1910 April 8 Crommelin-Cowell
 

But perhaps Halley's most important work was the part which he took in the publication of the "Principia." It was largely through Halley's influence that Newton was persuaded to prepare this great work for publication, and entirely at his expense that the printing was finally done.

Among the contemporaries of Halley, we find many astronomers whose names have survived in history. We need only mention Flamsteed, the first astronomer royal, Cassini, Hevelius, Koemer and Huyghens. In his sixty-fourth year, Halley succeeded Flamsteed as astronomer royal and, at once, boldly set about the task of observing the moon through a complete revolution of the nodes, viz., a period of